The present invention relates to a tantalum sputtering target and a method for producing such a tantalum sputtering target. In particular, the present invention relates to a tantalum sputtering target that is used for forming a Ta film or a TaN film as a diffusion barrier layer of a copper wiring in Large-Scale Integration (LSI), and to a method for producing such a tantalum sputtering target.
Conventionally, aluminum was used as the wiring material of semiconductor devices, but pursuant to the miniaturization and higher integration of the devices, the problem of wiring delay became an issue, and copper having smaller electrical resistance than aluminum is now being used. While copper is extremely effective as a wiring material, since copper itself is an active metal, there is a problem in that copper diffuses and contaminates the interlayer insulating film, and it is necessary to form a diffusion barrier layer made from a Ta film or a TaN film between the copper wiring and the interlayer insulating film.
Generally speaking, a Ta film or a TaN film is deposited by sputtering a tantalum target. As factors that affect the performance of a tantalum target during sputtering, it is known that the various impurities and gas components contained in the target, and the plane orientation and crystal grain size of the crystals affect the deposition rate, film thickness uniformity, generation of particles, and the like.
For example, Patent Document 1 describes improving the uniformity of the film by forming a crystal structure in which the (222) orientation is preferential from the position of 30% of the target thickness toward the central plane of the target.
Moreover, Patent Document 2 describes increasing the deposition rate and improving the uniformity of the film by causing the crystal orientation of the tantalum target to be random (no alignment to a specific crystal orientation).
Moreover, Patent Document 3 describes improving the deposition rate by selectively increasing the plane orientations of (110), (200), (211), which have a high atomic density, on the sputtering surface, and improving the uniformity by suppressing the variation in the plane orientation.
In addition, Patent Document 4 describes improving the film thickness uniformity by causing the variation in the intensity ratio of the (110) plane obtained based on X-ray diffraction, depending on the location of the sputtering surface, to be within 20%.
Moreover, Patent Document 5 describes that a round metal target having an extremely strong crystallographic texture such as (111) or (100) can be prepared by combining swaging, extrusion, rotary forging, and non-lubrication upset forging with clock rolling.
In addition, Patent Document 6 describes a method of producing a tantalum sputtering target by subjecting a tantalum ingot to forging, annealing and rolling, and, after processing the tantalum ingot into its final composition, performing annealing thereto at a temperature of 1173 K or less to obtain a tantalum sputtering target having a non-recrystallized structure of 20% or less, or 90% or less.
Moreover, Patent Document 7 discloses a technique of stabilizing the sputtering characteristics by causing the relative intensity of the peak of the sputtering surface of the target to be (110)>(211)>(200) through forging, cold rolling and other processes, and heat treatment.
In addition, Patent Document 8 describes forging a tantalum ingot, performing heat treatment two or more times during the foregoing forging process, additionally performing cold rolling, and performing recrystallization heat treatment.
Nevertheless, none of the foregoing Patent Documents describe the concept of reducing the discharge voltage of the tantalum sputtering target so that plasma can be more easily generated and suppressing the voltage drift during deposition by controlling the crystal grain size, or the crystal grain size and the crystal orientation, on the sputtering surface of the target.